1. Field of the Invention
The present invention relates to a blow mold comprising two mold halves pivotable about a common pivot axis and adapted to form an internal chamber for making a bottle and means for locking the mold halves relative to each other in their closed position.
2. Description of Related Art
Stretch blow molding machines utilizing such a blow mold are disclosed, for example, in West Germany Patent No. 3,336,071 or Japanese Laid-Open Patent Application No. 101137/1989. Since the two mold halves of such a blow mold are opened and closed in a pivotal motion, they can be rapidly closed after a preform has been inserted into the interior of the blow mold and rapidly opened after a blow molded article has been formed. This is very advantageous in that the cycle of blow molding can be shortened. The speed of operation in the stretch blow molding machines thus accomplished depends exclusively on the speed of each of the moving steps, that is, a step at which the mold halves are moved toward each other and locked relative to each other to close the blow mold and another step at which the mold halves are unlocked from each other and moved away from each other to open the blow mold.
In the conventional stretch blow molding machines disclosed in the aforementioned known literatures, the pivotal motion and locking/unlocking motion of the two mold halves were performed by the transmission of driving forces thereto from separate power sources. In such a case, these different motions were difficult to be harmonized with each other. It was particularly difficult to provide a harmonization between the movement of the mold halves into their closed position and the subsequential locking action on the mold halves and between the unlocking action on the mold halves and the subsequential movement of the mold halves into their open position.